The concave, snow-covered roof of a Moscow market collapsed early Thursday, killing at least 18 people and trapping about 10 people who were "knocking and crying out," Emergency Situations Minister Sergei Shoigu said. Rescue workers used pickaxes to cut holes in the wreckage of the roof, kneeling to call into the holes in search of survivors. Every few minutes, the more than 150 rescuers turned off their electric generators and stood silently to listen for signs of life. About five hours after the collapse, rescuers had located just one survivor. Moscow city prosecutor Anatoly Zuyev said up to 40 people could have been in the Bauman market in eastern Moscow at the time of the early morning collapse, Russian news agency RIA-Novosti reported. "We are working at full strength all over the territory of the market," said Yuri Akimov, deputy head of the Moscow department of the Emergency Situations Ministry. "Rescue workers are working underneath the building to save those still alive, and we are hoping to save the majority of them." The head of the Emergency Situations Ministry, Yuri Akimov, told state-controlled Channel One television that survivors were using mobile phones to help rescuers find them. Rescuers were also using sniffer dogs.